Electronic barrier



Oct. l1, 1960 K. H. SCHMIDT ELEcTRoNIc BARRIER 6 Sheets-Sheet 1 Filed July lO, 1957 .HIIHW w.

fniiiu INVENTOR SUM? ATTORNEY Ocf- 11, 1960 K. H. scf-:MlmI 2,956,269

ELECTRONIC BARRIER Filed July 10, 1957 6 Sheets-Sheet 2 INVENTOR W ge,

The BY YLMRR l Oct l1, 1960 K. H. SCHMIDT 2,956,269

ELECTRONIC BARRIER Filed July 10, 1957 6 Sheets-Sheet 3 raf/15475195' INVENTOR Oct. 11, 1960 K. H. SCHMIDT ELECTRONIC BARRIER 6 Sheets-Sheet 4 Filed July 10, 1957 INVENTOR c. e/vmccm,

ATTORNEY m IIIV Oct. l1, 1960 K. H. SCHMIDT ELECTRONIC BARRIER 6 Sheets-Sheet 5 Filed July 10, 1957 INVENTOR 0 n) m. i W w A 2 Zg/? im \\\\R\\\\\\ W ff ff .n0 w e T. u 6 h/ T mf. w T MM J AF NW T 4 A w S w. M c H m M MJ/f M w VG.. M W W m1 l E N m... /f w n4 m /m m 3 e@ @MAW/7 M m w M i M l W/ //d,/// M m R United States Patent ELECTRONIC BARRIER Kenneth H. Schmidt, Danbury, Conn., assigner to Mosler Research Products, Inc., Danbury, Conn., a corporation of Delaware Filed July 10, 1957, Ser. No. 671,013

18 Claims. (Cl. 340-258) My invention relates broadly to electronic security alarm systems and more particularly to an electronic security barrier or protective fence system.

One of the objects of my invention is to provide an electronic security alarm system which operates on the variations, in an induced electromagnetic eld, caused by the absorption or conduction of said lield by an intruding body.

Another object of my invention is to provide an electronic security alarm system which employs a protective fence or barrier comprised 'of a transmitting antenna or antennas to radiate an electromagnetic fieldr and an arrangement of receiving antennas responsive to' said eld.

Another object of my invention is to provide an electronic security alarm system in' which the receiving portions utilize no vacuum tubes, consume no power, require a minimum of service or maintenance and are eX- tremely stable.

Another object of my invention is to provide a security alarm system yrequiring a minimum of power and operating from a standard ll() volt A.C. line or from locally generated power.

Another object of my invention is to provide such an electronic barrier system which is applicable for both indoor and outdoor installations.

Another object of my invention is to provide a protective system which is capable of protecting large areas where the system is divided into a number of perimeter zones for the selective indication of conditions in the different perimeter zones.

Another object of my invention is to provide an electronic security alarm system which is self-compensating for changes in Weather and is therefore unatfectedV by variations in atmospheric conditions.

Another object of my invention is to provide such a protective alarm system which can be utilized in the irnmediate vicinity of high frequency transmitting antennas, without any loss in sensitivity or stability.

Another object of my invention is to provide an electronic security alarm system which is unaffected by transient interferences or variations in line' voltage.

Still another `object of my invention is to provide such a protective alarm system which is capable of initiating an alarm if any of its components breakdown or any physical damage occurs to the system.

Still another object of my invention is to provide means whereby a protective alarm system extending over `a substantial area is capable of having its functional operation manually checked from a central control point.

Still another yobject of my invention is to provide ia protective system which feeds a central indicator station enabling a guard at the indicator station to readily give electronic surveillance to the entire property under protection.

Other and further objects of my invention are set forth more fully in the specification hereinafter following by reference to the accompanying drawings, in which:

Fig. I is a simplied block diagram in schematic ar- ICC rangement of my electronic security barrier system and showing particularly the inter-related arrangement of the antennas which comprise the barrier or fence;

Fig. 2 is an `overall schematic view of the electronic security barrier system of my invention surrounding an area, and particularly showing the manner in which the barrier system may be divided into zones and the manner in which each zone is connected with a common guard station;

Fig. 3 is an electrical schematic diagram of the trans'-` mitting unit and loading coil for the electronic barrier system;

Fig. 4 is an electrical schematic diagram of a detector unit and a single zone guard unit used in the receiving system of my invent-ion;

Fig. 5 is an electrical schematic diagram of two guard units of the typeV designed to operate with central station operation, connected in a two zone protective system;`

Fig. 6 is a schematic diagram of the ground wire system for the electronic security fence system; j

Fig. 7 is an elevational View partly in transverse section, illustrating the construction of the outdoorv electronic fence of my invention and the manner of eliminating fence and tree interference by means of the common ground wire system;

Fig. 8 is an elevational view partly in section of the vertical type antenna fence employed in'an indoor installation and showing particularly the arrangement of the transmitting antenna with respect to theA receiving antennas;

Fig. 9 is a perspective View of the triangular outdoor type electronic fence installation `and showing particularly the arrangement =of the various antennas;

Fig. l0 is a detailed view partly in section of an insulator and insulator bracket secured to an antenna fence post and showing particularly the manner of keeping the antenna lines taut;

Fig. l1 is a perspective view of a double antenna fence post employed in dividing perimeter barrier zones;

Fig. l2 is a transverse sectional view of the zone dividing post sh'own in Fig. l1; and

Fig. 13 is a perspective view of a typical electronic barrier gate installation.

My invention is directed to the construction of an electronic security fence alarm system in which the wires or lines of the fence or barrier consist of a transmitting" antenna flanked by two receiving antennas. A transmitter, by means of the transmitting antenna, radiates an electro-l magnetic wave which is picked up by the' two receiving antennas. A detector is connected to each of the receiving antennas and the output voltage from -the detectors are balanced against one another so that the resulant signal is near zero magnitude and feeds into a very sensitive relay. The relay in turn signals the guard n an audio and visual manner. A

When an intruder approaches the electric field in the vicinity of the transmitting antenna, the signal to oneof the detectors either increases or decreases, depending upon whether such intruder is grounded or insulated from ground. This unbalance in the received signals disturbs the balanced voltage to the relay and the alarm is activated.

My electronic barrier alarm system invention is espe; cially applicable for large installations where it is impracticable to use such systems as photoelectric, capacity, audio, tape or other types. I have developed this system because there is a growing demand for a secure alarm system which can be used in large storage areas such as warehouses, largev factory buildings, hangars, magazine storehouses, storage depots, etc'.

'IheI advantagesV of the system of my invention operating on the induction principle over systems operatingon 3 Y a straight capacity principle are: (1) it does not entirely rely on the relation of the intruder to earth ground, therefore, it will detect as readily an intruder insulated from ground, such as on stilts, as one crawling on the ground, and v(2) the operation of the system is not affectedY by the type or. electrical properties of the local soil or ter-` rain. My system doesnot depend on the variationr of a delicate capacity balance of the system to ground. There is alsoa need for analarm system which can be utilized to form an electronic barrier or fence for outdoor use to be used in conjunction with the usual guard fence or existing guard fences instead of depending solelyon the -usual eight foot chain fence with barbed wire to keep out intruders.

By using the same style electronic fence as set forth above,rperimeter protection may be obtained inside a building or structure by running the antenna line along the wall. Thus it can be seen that my electronic antenna fence is applicable for both indoor and outdoor use. The modified outdoor electronic fence of my invention is arranged in va triangular design. With this design no Y other guard-fence need be employed with my electronic barrier since the possibility of an agile person jumping over or pole-vaulting over it is eliminated due to the wide Ybase design. Y

,. .Atmospheric weather conditions such as rain, sleet, hail or snow are a major consideration with any type of outdoor protection system. Variations in Vtemperature and humidity have noeifect on the sensitivity nor the stability of the electronic barrier of my invention. Because of its balanced detector circuit it is less aected hy` Weather conditions than any other alarm system, for what effects one receiving antenna likewise aiects the other, and the error voltageis cancelled out in the detector before it can cause a false alarm. Extreme weather conditions, such as hurricanes, severe ice storms or heavy snowfalls may in some instances put the alarm system temporarily out of commission.

In large outdoor installations, animals may present a problem where they are free to wander about and come close to or touch the antenna lines of the fence. However, small fences or high voltage shocking-type fences erected on either side of the electronic fence will Veliminate this problem.

In referring to the drawings in more detail, similar numerals refer to similar components throughout the specification. Y

The basic block diagram of my electronic security system is shown in its simplest form in Fig. l. It is comprised of atransmitting unit 2, located at any convenient position in the system where 110 volt A.-C. power is available, generally in the central station; transmitting antenna 1 installed along the perimeter of the area to be protected and supported on high frequency insulators; receiving antennas 3 and 4 installed on high frequency insulators along the perimeter of the area to be protected. With one receiving antenna on either side of the transmitting antenna, one pair per perimeter zone, and each pair no longer than 200 to 300 feet each, depending on Vthe terrain and zoning requirements; self-powered detector unit 15 consisting of detector circuit 5 associated with receiving antenna 3 and detector circuit 6 associated with receiving antenna 4, with one unit required for each pair of receiving antennas, therefore, one unit required per perimeter zone, Waterproofed and mounted on the fence posts of the antenna system; wires 7 and 8 of'any lengthY connecting the output of the detector unit with the guard panel 9; guard panel 9 located at the central station to provide audio and/or visual alarm notication, one being required per detector unit. y A master annunciatorunit is mounted with the guard panels to indicate by visual and/or audio annunciation, any transmitter-failure, connecting line tampering or accident, and if an emergencypowe'r supply is used 4 whether the transmitter and guard panels are operating on emergency power or on regular line power.

As mentioned hereinbefore emergency power supply can be associated with this equipment as an optional feature. It is a standard plug-in stand-by emergency power supply which takesrover automatically in case of power line failure and is capable of operating the system for a certain duration of time. Y Y

In Fig. 2 I have shown in schematic form, by utilizing the basic block diagram of my invention as seen in Fig.V 1, the manner in which an area can be protected with my electronic protective barrier system and the manner Y in which my perimeter protective system can be divided into zones to enable a guard to electronically identify the area of penetration quickly. Reference characters 10 and 11 indicate specic buildings, areas, etc., which are being guarded by my electronic fence alarm system. Guard house and central control point 12,- containing a 110 volt A.C. outlet, houses transmitting unit 2, guard panels 9a to 9e inclusive, and an annunciator unit and emergency power supplyfif used. Loading coil 13 is mounted on a fence post, as are detector units 15a to 15e, inclusive. V l Y In this illustration onlyone transmitter and one transmitting antenna 1 are utilized but if the perimeter of the area sgreater than 10,000 feet an additional transmitter or transmitters as well as additional transmitting antennas must be used.

. Here, for purposes of illustration, the perimeter is divided into five zones, namely, A, B, C, D and E. Each zone utilizes the common transmitting antenna 1, but supplies its own set of receiving antennas 3 and 4, detector unit 15 consisting of detectors 5 and 6, and guard unit 9. The detector lines (receiving antenna) 3 and 4 may be strung an estimated 1,000 feet per zone; however, in order for the' guard to'be able toV pin-point the area of entry, it is advisable to restrict each zone to approximately 200 to 300 feet. 'I'he length of a zone should actually be determined from the terrain, the distance from the guard point to the farthest point where entry could be made, periphery lighting, etc., and every zone need not be of the same length if it becomes desirable to have it otherwise. Because of the simplicity in the design of the detector units, adequate zoning becomes a desirable and'economical venture since each additional zone requires only a detector unit 15 at the fence and a guard panel 9 at the guard station.

To illustrate the practicability `of the perimeter zoning, assume an intruderapproaches the protected area somewhere along the fence line of zone C; this substantially disturbs the electro-magnetic field set up by the transmitting antenna 1 and the signal to one of the receiving antennas 3c or 4c either increases or decreases. This produces anunbalanced signal output between detectors 5c and 6c and an error signal is sent to guard panel 9c; the guard alarm relaythrows, setting oi the alarm and lighting a light indicating an intruder is approaching or penetrating the area somewhere along zone C. The guard is now able to go to the exact zone of intrusion to Vtake immediate preventive measures rather than having to check the perimeter around the entire area. A standard chain link fence 14 or the like may -be employed with my electronic security'fence, depending upon which style of electronic outdoor fence is employed, as will be discussed hereinafter.

The schematic diagram of the transmitting unit 2 and its associated loading coil 13 which are employed in my invention are'shown in Fig. 3. The transmitter includes an oscillator which consists of oscillator coil 57 rand frequency tuning condenser 58 coupled by means of network 59 to oscillator tube 16 whoseroutput in turn is fedV back to the frequency tuning circuit by feedback resistor 60. output is also fed by means of coupling condenser 61'and output control potentiometer 17 to amplifier-in- Vcltivl of the twin triode type. Output control potentiometer 17 is used to adjust the sensitivity of the system since .it controls the transmitter ouput.

iThe transmitters output radio frequency is supplied at terminals 19 and 20 of output matching transformer 21 whose primary winding is connected in the plate circuits of the output power amplifiers 22 and 62. These ampliers are connected by means of a balanced push-pull circuit network 63 to the intermediate amplifier-inverter 18.

The primary winding of power transformer 23 is supplied by standard 110 volt A.C. voltage, and its secondary winding supplies B+ power for the transmitter through fullwave rectifier 24, choke input filter network 25, voltage drop resistor 56, and voltage regulator tube 26. The transmitter on-otf switch 27 is situated in the input power line. The output of the transmitter is constant at very low radio frequencies in the range of 15 to 30 kilocycles per second wherein atmospheric conditions such as the positions of the ionosphere, sun spots, magnetic storms, etc. have a negligible eiect on the radiation characteristics of these radio waves. The output of the transmitter has been stabilized to a very high degree so that variations of line voltage, line failure, changes in tube characteristics, etc., do not affect the R.F. power output from the transmitter. The choice of frequency in the range of 15 to 30 kc./second provides a desirable radiation pattern from the antenna wherein the eld strength is very rapidly attenuated at short distances from the transmitting antenna and therefore no interference is produced that would effect the reception of long range, highly sensitive communications, receivers or other electronic equipment in the immediate vicinity.

As mentioned above, potentiometer 17 adjusts the sensitivity of the system. At maximum sensitivity setting the alarm signal would be initiated when an intruder came Within six to eight feet of any antenna line, either transmitting or receiving. The average sensitivity setting usually provides a range of three to four feet for detection.

The transmitter loading coil is designated by reference character 13 and of course the components vary according to the length of transmitting antenna line used so as to make resonation of said loading coil possible. The loading coil is encased in a waterproof housing and mounted on the antenna fence post.

A single transmitter may drive as much as a 10,000 foot run of antenna line. Longer lengths may be accommodated by using an additional transmitter.

The functional operation of the system can be tested from the control station by using the test point 28 on the transmitter. When test terminal 2S is grounded the power of the antenna radiated eld is decreased appreciably. Since the detectors are tuned for a certain range of antenna radiated power this abrupt reduction in power will create a detector unbalance signal in every zone and initiate an alarm at all zones through the guard panel relays, thus indicating that the system is operational. The severity with which the alarm goes off may be controlled by the test potentiometer 29 in the transmitter circuit since it controls the transmitter output power when test terminal 28 is grounded. This potentiometer is adjusted so that the guard unit alarm relay 36 .is just barely actuated.

The transmitter antenna 1 and the receiving antennas 3 and 4 are constructed of any electrically conductive material applicable for such purpose. Plastic covered copperweld is an excellent material with which to construct such antennas.

It can be seen from Fig. 4 that the detector unit 15 does not utilize any electron tubes, or 110 volt A.C. line power, and therefore consumes no power. The signal received by the receiving antennas is strong enough to operate the sensitive rel-ay, in the guard unit, Without previous amplification. A detector unit consists of detector circuit 5 which is associated with receiving antenna 3, and detector circuit 6fwhich is associated with receiving antenna 4. The firstY stage of the detectors consist of high Q tuned circuits consisting of parallel combinations of balancing resistors 30, xed tuning condensers 31', trimmer condensers 32, and high Q tuned transformers 33; The values of fixed condensers 31 vary with the receiving antenna length and are such as to resonate the detectors at convenient settings of trimmer condensers 32. The second stage of the detectors consists of half-wave rectier diodes 34 and 35, and iilter condensers 37, which feed the rectied direct current directly into the balanced alarm relay circuit of the guard unit, by means of wires 7 and 8.

Because of the high Q tuned transformer and the large amount of capacity built up by the receiving antenna (between 500 and 1,000 mmf.) broadcasting and short wave radio transmitters as well as transient interference caused by leaky fluorescent fixtures, motors', high voltage line transformers, arcing or even lightning discharges have no elect on the system.

Since in all installations the receiving antennas are placed -equidistant from the transmitting antenna they each receive the same strength signal. When the detector circuits are resonated they are tuned so that the output Voltage from each detector circuit is brought almost to zero balance with respect to the other. If the output voltages were completely and accurately balanced out, any atmospheric condition would affect each' detector exactly the same, and the change would be cancelled out completely. This would be a very stable point of operation; however, the system is not set up in this manner because it is necessary to haveV the alarm actuated upon failure of the transmitter signal. To permit this the signals are tuned just slightly out of balance So that if the transmitter fails the diiference betweenV the' slightly unbalanced signals disappears. The guard unit ,is adjusted so that the disappearance of this small signal is suiiicient error signal to actuate the alarm.

When an intruder approaches the induced electromagnetic iield, set up by the transmitted RF energy and received in equal strength by each receiving antenna, the presence of his body, :if grounded, will absorb and ground part of the electromagnetic tield, thus lincreasing the signal received by one of the antenna, or decreasing the signal received by one more than that received by the other. lf the intruders body is insulatedV from ground, above ground, he will, by conduction of the electromagnetic field, increase the signal received by one antenna more than that received by the other. When either of the above happens the small unbalance signal which has been tuned into the circuit either increases or' decreases depending upon the situation, resulting in a change of current from the output of transformer 33, and either a positive error signal will be sent to terminal 1 or a negative error signal sent to terminal 2 of the balanced alarm relay circuit in the guard unit. This error signal is suicient to actuate the sensitively balanced` alarm relay, and thus the alarm is set off.

Two types of guard units 9 can be used with my fence alarm system. The rst type, shown in'Fig. 4, is'designed to operate with a proprietary system and has a normal type of reset on alarm relay 36 which must be reset by the guard on duty once the alarm has been initiated.

The guard unit balanced alarm relay circuit consists of filter condensers 38, coils 39, of vline relay 40, compensation capacitor 41, and alarm relay 36; Error signals are admitted to the circuit through either terminal 1 or 2', depending on whether the signal is positive'y or negative. With the Day-Night Select switch 42 in the Night position, if an error signal is received by the balanced relay circuit, alarm relay 36 will throw grounding B+ through the coil of slave relay 43.- In turn, the contacts of slave relay `43 move to points 44 and 45 putting B-iacross light 46y and buzzer 47 thus actuating them and registering the alarm; simultaneously putting a short circuit across the coil of alarmy relay 36 through contact point 44, thus de-activating it and protecting it since it is a delicate relay.

A s mentioned hereinbefore, alarm relay 36 must he manually reset to cease the alarm, even though its coil hasV a short-circuit across it. When relay 36 is reset slave relay 43 is de-energized and its contacts return to their original position, thus silencing the alarm. Buzzer 'silencer switch 48 is provided to cut out buzzer 47.

During the day, switch 42 is put in the Day position, thus interrupting the balanced alarm relay circuit. In this situation an error signal will activate the singlepole double-throw line relay 40,*thus activating light 49 by impressing B+ across it.

I have shown the electrical schematic diagram of my other type guard unit in Fig 5. Here two guard units are shown indicating the area protected is divided into a two-zone system. This type guard panel is designed to operate with central station operation and by comparing it with the type shown in Fig. 4, it can be seen that their circuitry is basically vthe same. This latter type has 'more terminals brought out to enable a master annunciator unit and/or an emergency power supply unit to be connected if desired. This unit has a common, normally open 44 and 45' and normally closed contact arrangement in slave relay 43', whose contacts may be wired together with the tamper switch into whatever circuitV is to be used, by means of leads 4', 9', 8 and 10 which Vare brought out from said relay 43. An auto- 'matic reset circuit Vis employed with alarm relay 36 in this type guard unit rather than the manual reset operation as set forth under Fig. 4. This automatic reset circuit is composed of resistors 54, 55 and capacitor 51 which compose a time delay circuit, and the single-pole double-throw reset relay 50 whose coil 52 is controlled by the time delay circuit. Reset relay 50 activates reset coil S3 which in turn resets Valarm relay 36 after the delay Ytime has elapsed after an alarm has Ibeen initiated. The guard panel has been designed by utilizing line relay -40 so that the alarm relay resetting mechanism will not operate, if there has been a transmitter power failure, a Ibroken fence line, a fence line grounded, or a broken line between the detector and the guard panel, so a malfunction condition indication will remain until the trouble is cured since relay 36' cannot be reset.

When the guard panel 9 and transmitter unit 2 are VAnot located together a separate B-ipower supply is needed to operate the guard panel since it normally gets its B-land B- supply from the transmitter unit 2.

The guard unit system of a typical outdoor installation of a vertical type electronic security fence used in conjunction with a chain link fence is shown in Figs. 6 and 7. Fig. 6 is a top schematic view, while Fig. 7 is a transverse sectional view of such an installation. Since any object in the immediate vicinity of the electronic 'fence would aect the field radiated by the transmitting antenna and thus the signal'received by each of the receiving antennas, every object and obstacle in close proximity to the fence must be grounded before the detector units are resonated and balanced. Chain link fence 14, Vertical antenna posts 66, and obstacles such as trees l67 are all grounded in a common ground system network by ground wires 64 and ground posts 65. The transmitter, loading coil, detector units and guard units are also connected into this common ground system. Fig. 7 `also illustratcsthe construction and arrangement of the various antenna on the vertical type outdoor antenna fence of my invention. The antenna lines are Ysupported 'on high voltage insulators 68 which are attached to4 the Y fence posts 66 by insulator arms 69. The bottom receivving antenna or detecting wire 4 is installed approximate- `ly sixteen inches above the ground, while the top detect- Aing antenna or wire 3 can be six feet to eight feet above AthevV ground with the transmitting antenna'or wire 1 lcentered between the two. Since the receivingv antenna Vlines'3 and 4.are equidistant from'the transmitting antenna 1 they both receive thesame signal strength. Using'this vertical type outdoor electronic fence, the transmitting and detector lines are installed along the perimeter of the area to be protected preferably several feet inside a guard fence 14, as illustrated in Fig. 2.

l Peripheral protection indoors may be accomplished easily and economically by running the antenna lines horizontally one above the other, that is, 3 or 5 (wherein generally 1 is the transmitting antenna and 4 is the receiving antenna) along the walls, across the windows, louvers, gates and other passages by using detachable lines where necessary, in such a manner that the complete wall area of the building would be protected. I have illustrated the manner of installing such a system in Fig. 8. It can be seen that this arrangement is identical to that used in the vertical type outdoor fence as seen in Fig. 7.

Barrier protection between one part of a building and another without the construction of walls may be accomplished in a similar manner by running a sufficient number of antenna lines horizontally one above the other, spaced about three to six feet apart, across from one wall to the other, to cover the area from oor to ceiling in such fashion that any unauthorized approach or any intrusion would actuate an alarm.

A modified form of my outdoor electronic fence is shown in Fig. 9. The vertical post 70 extends approximately six feet to eight feet above ground, as desired, and has mounted approximately fourteen inches above ground a sixV foot to eight foot cross-arm 71 or a high grade commercial high frequency insulator. An insulator 68 is mounted on each end of this cross-arm as well as one on top of pole 70. Transmitting antenna 1 is installed as the top line'so it will be equidistant from receiving antennas 3 and 4 in the relationship of the outline of an isosceles triangle with reference to the receiving antenna. Y

With this triangular outdoor antenna fence no high guard fence 14 need be employed since the wide base design (six to eight feet between receiving antennas 3' and 4') eliminates the possibility of an agile person jumping over or pole-vaulting over it. If such an incident occurred the pole-vaulter or high jumper would find himself forced to descend between the transmitter and detector'lines. For the non-athletic person entry is impos- `sible exceptby tunneling or use of a very high bridge.

at the end or beginning of a straight run, and the manner of attaching insulator arm 69 to antenna post 66 by means of bolts 7S. The antenna is attached to strain insulator 72 which in turn is attached to spring 73 which is secured to insulator 68. This arrangement spring loads the antenna lines and maintains them taut to prevent swaying in a gusty wind, since such an occurrence may be sufficient to cause a false alarm. Rapid flutter or vibration of taut lines does not aect the operation of the system because the alternating voltage produced in this manner is ltered-out before it becomes troublesome.

Lead-in coaxial cable 74 is secured to insulator arm 69 at point 76, and the antenna line at point 77 after suiiicient slack has been provided. This lead-in coaxial cable may extend from the transmitter loading coil or it may constitute the output to a detector unit, whichever the case may be. The same symmetrical arrangement is used in each case.

In Fig. ll I have shown an elevational View of a zone dividing vertical type antenna fence post 66', while in Fig. l2 I have shown the same fence post in a transverse sectional view. ThisV zone post 66' is a double post and like the single post 66 is approximately eight feet high and made of steel or equivalent suitable material.

Y Since the detector unit 15 can be placed at either end vof the receiving antennas 3 and 4, here I have shown it 9 'connected at the beginning of the ione. The beginning of the irst zone is to the left in the illustration While the end of the last zone is to the right.

Since the last zone terminates on the right the receiving antennas 3 and 4 will terminate at the insulators 68 as shown. As illustrated here all antenna lines are spring loaded at the beginning of the zones.

Coaxial lines 78 and 79 connect detector unit 15 to receiving antenna lines 3 and 4, respectively. Wires 7 and 8, as mentioned earlier, connect the detector output with the guard panel 9.

Transmitter loading coil 13 mounted on the fence post is connected to transmitting antenna 1 by means of wires 80 and to the transmitter by coaxial line 81. Here the loading coil 13 is shown connected to a position other than' an end of the transmitting antenna. The loading coil and detector unit are connected to the common system ground wire 64 which follows the antenna fence around the protected area.

In Fig. 13 -I have shown a typical gate installation of my vertical type outdoor antenna fence. The gate as shown here appears in the middle of a zone which proceeds from right to left. The antenna lines are terminated at the insulators on the extreme right. Coaxial lines 83, 84 and 85 connect to the terminated ends of antennas 3, 1 and 4, respectively, and are laid in conduit 82 underground beneath the gate access area. These lines emerge from the conduit on the left and are reconnected with their respective antenna lines as shown. To form the gate, connecting lines 83', 84 and 85 connect antenna lines 3, 1 and 4, respectively to gate antenna lines 3, 1" and 4", respectively. These gate antenna lines are attached to insulators 68 by means of insulated spring handles 86 to permit easy detachment of said gate antenna lines to permit access to the protected area.

I have held-tested my electronic fence security alarm system in actual installation and it has proven itself to be a secure, stable alarm system capable of accomplishing in a practical way things that no other alarm system will accomplish. I realize, however, that modifications may be made, and I desire that it be understood that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intru- .sion of said protected area, comprising in combination with a radio frequency transmitter, a .transmitting antenna vsystem extending coincidentally with the perimeter to be protected, and connected to said radio transmitter, a pair -of receiving antennae spatially related to said transmitting :antenna system symmetrically on each side thereof, a detection system connected with said receiving antennae and means for indicating conditions of abstraction or conduction of energy from the field of said transmitting antenna system with respect to said receiving antennae.

2. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 1, in which said symmetrically disposed receiving antennae are :arranged laterally equidistant from said transmitting :antenna system.

3. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating .means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 1, in which said symmetrically disposed receiving antennae lextend parallel to said transmitting antenna system, both of said receiving antennae being contiguous with at least a portion of said transmitting antenna system.

4. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrui` sion of said protected area, as set forth in claim 1, in which there are a plurality of pairs of receiving antennae disposed symmetrically on each side of said transmitting antenna system each of said pairs of antenna being individually connected with separate detection systems and associated means for indicating conditions of abstraction or conduction of energy of the iield of said transmitting antenna system With respect to each pair of receiving antennae, the said transmitting antenna being common to all of said pairs of receiving antennae.

5. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 1, in which said detection system includes a multiplicity of tuning means, one of said tuning means being connected with one receiving antenna and another of said tuning means being connected with the other receiving antenna of said pair of receiving antennae, the frequency of said tuning means connected with one receiving antenna being offset from the frequency of said tuning means connected with the other receiving antenna of said pair of receiving antennae.

6. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 1, in which said transmitting antenna system and said pair of receiving antennae are spatially related in such a manner that a cross-section of said spatial relationship is an isosceles triangle with the base thereof extending substantially parallel with the plane of the terrain.

7. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim l, in which said transmitting antenna system is disposed between said pair of receiving antennae and all disposed in the same vertical plane.

8. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim l, in which said transmitter includes an output circuit and test means connected to said output circuit for checking the operational state of said systems.

9. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, comprising in combination a central indicator board for indicating conditions throughout the perimeter of the protected area including independent indicator means, independent signal receivers, one indicator means being common to a signal receiver and containing a balanced alarm relay circuit, a pair of signal detecting circuits in each signal receiver, a receiver antenna individual to each of the signal detecting circuits of each signal receiver, a radio transmitter, a transmitting antenna system connected with said radio transmitter and extending peripherally of the protected area, the pair of receiving antennas of each signal receiver being symmetrically disposed in spatial relation on each side of said transmitting antenna system, the signal detecting circuits in each signal receiver being responsive to changes in current in Said receiving antennas incident to the presence of the body of an intruder in the iield of said transmitting antenna.

l0. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 9 in which said balanced alarm relay circuit of said independent indicating means includes two reset relay Wind- 11 ings, said windings being disposed in series and connected in shunt with the output of the signal detecting circuit.

1l. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intru- Sion of said protected area, as set forth in claim 9 in which the state of said balanced alarm relay circuit of said independent indicating means is controlled by the conditions of `abstraction or conduction of energy of the field of said transmitting antenna system in the perimeter zone associated with said indicating means.

12. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 9 in which said balanced alarm relay circuit of said independent indicating means includes compensating means enabling said balanced alarm relay circuit to detect a failure of said radio transmitter or transmitting antenna system.

13. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrustion or intrusion of said protected area, as set forth in claim 9, in which said balanced alarm relay circuit of said independent indicating means includes an alarm relay and automatic reset means for resetting said alarm relay after it has been activated.

14. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 9, in which an automatic reset means associated with said balanced alarm relay circuit of said independent indicating means Will not operate to reset said alarm relay circuit until-the activating cause of energizing said relay circuit is removed.

l5. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area comprising in combination a radio frequency transmitter, a transmitting antenna system extending coincidentally With the perimeter to be protected, and connected to said radio transmitter, a plurality of pairs of receiving antennae spatially'related to Ysaid transmitting antenna system symmetrically on each side thereof and consecutively disposed along the length thereof forming separate perimeter zones about said transmitting antenna system, a plurality of pairs of signal detection circuits located in said separate perimeter zones, said plurality of pairs of signal detection circuits in said separate perimeter zones connected to said plurality of pairs of receiving antennae in the same separate perimeter zones, and a central indicator board connected with said pairs of signal detection circuits and operating to indicate positional location of intrusion at any one of the Zones.

16. An electronic security alarm system for perimeter protection of an area and for transmitting -to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 15, in which any perimeter Zone or zones includes gate openings provided with antennae protection means across same, such antennae being an extension of the antennae systems of the zone or zones in which the gates are disposed.

17. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set for in claim 15, in which any perimeter zone or zones may include gate openings provided with a transmitting antenna portion and a pair of receiving antennae portions electrically contiguous with the corresponding antennae of the related zone or zones.

j 18. An electronic security alarm system for perimeter protection of an area and for transmitting to indicating means an indication of an attempted intrusion or intrusion of said protected area, as set forth in claim 15, in which there are gate areas located laterally of said transmitting antenna system and said receiving antennae and wherein the antennae of the zones in which the gate areas are arranged underground in the gate area to provide uninterrupted antennae perimeter zones.

Rubenstein Aug. 8, 1944 Peck Sept. 30, 1947 

